Hydrogen adsorption and reaction on RuO2(110)

Abstract

Ruthenium dioxide is used extensively as a co-catalyst in a wide range of photocatalytic water splitting systems. As such, understanding how it promotes the evolution of hydrogen and oxygen is of high importance. In this study, we employ scanning tunneling microscopy to study the adsorption and reaction of hydrogen on a model RuO2(110) surface. We find that at low coverages H2 dissociates heterolytically to hydride‑hydroxyl pairs even at 5 K. The onset temperature for the low coverage H2 dissociation is surprising as it is not expected based on prior temperature programmed desorption studies. At higher coverages, H2 chemisorbs molecularly on bare ruthenium sites that are neighboring the hydride‑hydroxyl pairs. Upon annealing, the chemisorbed H2 disappears by 120 K, primarily due to H2 desorption from the surface. Further annealing between 120 and 295 K leads to the conversion of hydride species to bridging hydroxyls. The bridging hydroxyls ultimately recombine between 450 and 600 K to form water, yielding clean RuO2(110) with oxygen vacancies.